Microwave noise source standard



INVENTQR ll iNNNNaNNk 2 Sheets-Sheet 1 R. H. GEIGER MICROWAVE NOISE SOURCE STANDARD June 11, 1968 Filed March 51, 1967 4 Ww m m 8 k m M 2. 0 mm June 11, 1968 R. H. GEIGER 3,388,341

MICROWAVE NOISE SOURCE STANDARD Filed March 51, 1967 2 Sheets-Sheet 2 United States Patent 3,388,341 MICROWAVE NOISE SOURCE STANDARD Richard H. Geiger, Stamford, Conn, assignor, by mesne assignments, to Signalite Incorporated, Neptune, N.J., a corporation of New Jersey Filed Mar. 31, 1967, Ser. No. 627,432 14 Claims. (Cl. 331-78) ABSTRACT OF THE DISCLOSURE The disclosure relates to a gas discharge noise source standard including a gas discharge tube for generatingmicrowave noise energy and a mount for coupling this noise energy to one or more output ports as a calibrating signal. The gas discharge tube is formed having a quartz envelope backfilled with xenon. The quartz envelope at the cathode end of the discharge tube is enlarged to increase the xenon fill volume to envelope surface ratio. The cathode structure is heated for improved operating efliciency and shielded for long life. The mount is formed of oxygen-free, high conductivity (-OFHC) copper and is backfilled with a non-oxidizing gas. The insertion angle between the mount and the tube positive column is 7 degrees.

The present invention relates to generators of electromagnetic energy at microwave frequencies. More particularly, it relates to improvements in microwave power standards. The most widely accepted source of constant microwave energy for use as a working power level standard is the gas discharge tube. As is known, an electrical discharge through a gas medium produces electromagnetic energy which is totally random, with uniform and continuous energy distribution throughout the frequency spectrum. Such microwave energy is commonly referred to as noise or white noise. This invention is specifically directed to improvements in gas discharge noise sources, and to improvements in gas discharge tubes and microwave energy coupling circuits used therein.

There is increasing need among manufacturers in the microwave field for a reliable working noise source standard which can be used to accurately determine certain performance characteristics of their products. As the term standard implies, such noise sources must provide a known noise power output which remains precisely constant for long periods of time. The National Bureau of Standards is in the process of expanding its facilities for calibrating microwave noise sources. Once a microwave noise source is calibrated and certified by the National Bureau of Standards, a procedure involving significant time and expense, it would be most desirable to have the noise power output remain constant over a reasonably long period of time. Stability with age is, of course, a measure of a noise standards reliability. It is obviously of great importance for the microwave industry to have reliable, certified Working noise standards for use as measuring tools, for it is only in this way that misunderstanding and confusion can be avoided. Otherwise, as is unfortunately the situation plaguing the microwave industry today, there is no common yardstick to go by.

There are two distinct aspects to be considered in developing a reliable noise standard. One is the gas discharge tube itself which constitutes the generator of the noise power. This generator must produce noise at an unvarying, repeatable power level and continue to do so with long life. The other equally important consideration is the means, typically referred to as the mount, by which the noise power developed by the gas discharge tube is coupled to the microwave system to be measured.

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If this coupling deteriorates with age, the noise power available at the mount output will not remain constant regardless of the stability with age of the gas discharge tube. Then, too, the cold loss of the mount should be low and invariant so that maximum noise power of a constant level is available at its output.

It is accordingly an object of the present invention to provide a reliable gas discharge noise source standard.

An additional object is to provide a microwave noise source standard of the above character wherein the available noise power output remains precisely constant.

Still another object of the present invention is to provide a noise source standard of the above character having long operating life.

A further object is to provide a noise source standard of the above character whose available noise power output is unvarying and repeatable.

A still further object is to provide a noise source standard of the above character which is virtually unaffected by aging.

Yet another object is to provide a noise source standard of the above character which is eflicient in operation.

Another object is to provide a noise source standard of the above character having extremely low energy loss characteristics.

A further object is to provide a gas discharge tube for use in a noise source standard of the above character.

Yet another object is to provide a mount for use in a noise source standard of the above character.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combinations of elements, and arrangements of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side elevational view of a gas discharge noise source standard constructed according to the invention;

FIGURE 2 is an enlarged partial sectional view taken along line 22 of FIGURE 1 to show the anode and cathode constructions of the gas discharge tube;

FIGURE 3 is a side elevational view of an alternative embodiment of a noise source standard constructed according to the invention; and

FIGURE 4 is a graph illustrating the operation of the invention.

Broadly stated, the present invention provides a reliable gas discharge noise source standard which includes a gas discharge tube of novel construction operating to generate noise energy and a microwave mount, also of novel construction, operating to couple this noise energy to one or more output ports to be available for use as a calibrating signal. The gas discharge tube, according to one feature of the invention, is constructed having a tube envelope made of quartz, rather than glass. Quartz is considerably less lossy to microwave energy, thereby making more noise power available at the output(s) of the mount.

As an additional important feature of the invention, the gas discharge noise tube is filled with xenon rather than argon as is commonly used. Of the rare gases, xenon is found to have the lowest ionization potential and critical current characteristics. The critical current is that current through the discharge above which lowfrequency plasma oscillations are substantially absent. Thus, less DC voltage is required to initiate an electron discharge in xenon, and less DC power input is required to sustain the electron discharge. Consequently, less DC power is expended in operating a xenon-filled noise tube, thereby extending its operating life. In addition, xenon, being a heavy gas, has a lower rate of diffusion into the tube envelope and other tube parts as compared to the lighter argon gas. The pressure of the gas fill, which has an effect on the noise power developed by any discharge tube, will remain more substantially constant over the life of the tube when xenon is used.

A further feature of the invention resides in the use of a hot cathode rather than a cold cathode typically used in gas discharge noise tubes. Use of a hot cathode materially lowers the cathode work function with the result that less DC power input is required to initiate and sustain the electron discharge in the tube. Moreover, longer life of the cathode element is achieved. The hot cathode of the novel gas discharge tube is shielded to enhance thermal efficiency and also to protect the cathode from bombardment by positive ions.

As a further feature of the invention, the tube envelope is formed having an enlargement at the end of the tube. This enlargement provides a reservoir for the xenon gas fill. The volume of this reservoir is at least ten and preferably one hundred times greater than the volume of the positive column or active portion of the discharge tube. This reservoir serves not only to accommodate the shielded hot cathode construction but also to increase the gas fill volume to envelope surface area ratio. As the rate of diffusion of xenon is fixed, the change in gas pressure is still further lowered, and the fill pressure remains more constant with age. Moreover, the effects of ambient temperature changes on the discharge tube operating characteristics are minimized.

Also included within the tube envelope enlargement is a porous ceramic capsule containing a getter. The idea of using getters in gas-filled tubes for the purpose of absorbing impurity gases is well known. However, as a feature of the invention, the capsule contains micro-fine uranium dust which is found to be a more effective getter than any of the other commonly used getter materials.

As still another feature of the invention, the waveguide mount for coupling microwave noise power from the plasma column, the gas discharge tube is made of oxygenfree, high-conductivity (OFHC) copper. This material is virtually lossless as compared to other microwave waveguide materials such as silverplated brass. OFHC copper waveguide has an extremely low cold insertion loss, thus providing maximum available noise power at the output port( s) of the waveguide.

In addition, the angle of insertion of the plasma column or active portion of the gas discharge tube relative to the output waveguide is made smaller than in prior art microwave noise source mounts. The insertion angle in prior art devices is typically degrees. According to the present invention, the insertion angle is reduced to 7 degrees. As a result, the plasma column of the gas discharge tube is more perfectly matched to the output waveguide, and a lower voltage standing wave ratio (VSWR) is achieved.

A further feature of the present invention resides in providing a non-oxidizing gas fill in the output waveguide. This non-oxidizing gas prevents oxidation of the inner surfaces of the output waveguide. Oxidation increases the insertion loss of the output waveguide, thus decreasing the available noise power output with age. To contain this non-oxidizing gas fill, a thin membrane( s) is made of a material, such as Teflon or quartz, which is practically lossless to microwave energy.

Of the two embodiments of the invention disclosed, one is a double-ended version wherein the waveguide has two output ports. The other embodiment is a single-ended version having one waveguide output port from which the noise power output is obtained. In the single-ended version, it is desired to include in the mount a waveguide load at the other end of the output waveguide from output port. This waveguide load is adapted to absorb virtually all noise power propagated through the waveguide in its direction. In addition, this waveguide load serves as a matched impedance in the absence of a discharge plasma to the equipment under test connected to the waveguide output port.

Referring now to the drawings, the single-ended microwave noise source standard show in FIGURE 1 as one embodiment of my invention includes a microwave iount, generally indicated at 10, supporting a gas discharge noise tube, generally indicated at 12 in FIGURE 2, relative to an elongated, rectangular, microwave waveguide 14 coupling noise energy to an output load, not shown. The mount It) includes, in addition to the waveguide 14, a cylindrical housing 16 containing the cathode end portion, generally indicated at 18, of the gas discharge tube 12 (FIGURE 2). The anode end portion, generally indicated at 26 in FIGURES l and 2, is spaced from the cathode end portion 18 by an elongated, tubular envelope section 22 termed the active portion or positive column of the gas discharge tube 12. It is through this positive column 22 that the electron discharge occurs to develo therein the plasma responsible for the genera tion of noise power.

The positive column 22 of the gas discharge tube 12 projects through elliptical apertures 24 and 26 formed in the upper and lower broad faces and 27 of the microwave waveguide section 14. This manner of introduction of the positive column of a gas discharge tube to a microwave waveguide is referred to in the art as E-plane insertion. An open-ended tubular section 28 encompasses the portion of the positive column 22 extending between the waveguide 14 and housing 16. This section is afiixed at one end about the elliptical opening 24 in waveguide wall 25, while its other end is affixed about an opening in an end wall 30 of housing 16 through which the positive column 22 extends. A second tubular section 32 has one end affixed about the elliptical opening 25 in waveguide wall 27 and extends to encompass and support the portion of the positive column 22 between waveguide 14 and the anode end portion 20 of the discharge tube 12.

As generally noted above, one of the features of the invention resides in the angular relationship or insertion angle of the positive column 22 of tube 12 relative to the waveguide 14. This insertion angle, indicated by the reference numeral 33 is, according to my invention, established at substantially 7 degrees. This 7 degree insertion angle, as compared to the 10 degree insertion angle invariably used in prior art noise source standards, provides for a tighter coupling of the noise power generated by the plasma existing in the positive column 22 into the waveguide 14. The discharge plasma and the waveguide are more nearly matched, resulting in a significant reduction in the voltage standing wave ratio (VSWR) over the operating bandwidth determined by the dimensions of the waveguide. This lower insertion angle also provides a more gradual transition from the discharge plasma to the waveguide 14 for the noise energy. Furthermore, the lower insertion angle tends to reduce the effects of oscillations occurring in the discharge plasma by reducing the low-frequency impedance changes in the vicinity of waveguide apertures 24 and 26 due to possible density modulation of the electron discharge in the tube 12. As will be seen below, the invention includes provisions calculated to eliminate the possibility of any such oscillations occurring.

The noise power generated by the discharge plasma in the positive column 22 propagates to the left in waveguide 14 as seen in FIGURE 1 and exits from an output port 34. A waveguide flange surrounding output port 34 facilitates connection to the equipment under test. Closely spaced from the waveguide flange 35 is a diaphragm 3S stretched transversely across the waveguide 14 and clamped in place between waveguide flanges and 4 3. The diaphragm 38 is formed from a suitable material such as Teflon or quartz, which are essentially lossless to microwave energy. In other words, the diaphragm is a window transparent to microwave energy and, thus, passes noise power substantially unattenuated to the output port 34.. The purpose of the diaphragm 38 is to permit removal of air from the interior of the waveguide 14 and the substitution of a suitable nonoxidizing gas such as nitrogen. As the Waveguide oxidizes, it becomes increasingly lossy to microwave energy, i.e. its cold insertion loss increases. The non-oxidizing gas fill in waveguide 14 prevents oxidation, thereby maintaining the insertion loss essentially constant with age. Thus, the noise power conducted through the waveguide 14 remains essentially constant with age.

It is preferred that the non-oxidizing gas fill in the waveguide 14 have some slight positive pressure which can be readily withstood by the diaphragm 38. This will tend to prevent air from entering the waveguide 14. As a check on the integrity of this gas fill, a pressure auge 42 is included. A pressure drop indicated by gauge 42 will give notice to the user that the non-oxidizing gas fill is leaking out, thereby jeopardizing the constancy of the noise standard.

The waveguide 14 is fabricated from oxygen-free, highconductivity (OFHC) copper. OFHC copper waveguide has extremely low loss characteristics to microwave energy and thus extremely low insertion loss. Noise energy generated by a gas discharge tube is at an extremely low power level at best, typically in the micro-microwatt range. The low insertion loss of waveguide 14 makes available more noise power at output port 34 than would be available using a conventional silver-plated base microwave waveguide.

Returning to FIGURE 1, a waveguide load 4 in the form of a suitably absorbing wedge is mounted in the end of waveguide 14 terminating in the end wall 36 of housing 16. The purpose of this waveguide load 44 is to absorb with negligible reflection the noise power propagated in its direction. The principle function of the load 4 is to present a reasonably matched impedance to the input circuit of the equipment under test when the discharge plasma is terminated. With the tube operating, the discharge plasma acting as a resistor matched to and across the waveguide 14 appears as matched impedance to the equipment. Without the load 44, the impedance seen by the equipment would go from a matched value with the tube 12 on to essentially zero when the discharge is terminated. This situation presents the possibility of serious measurement error, but is avoided by the inclusion of the load 44.

Turning now to the construction of the gas discharge noise tube 12, the enlarged cathode end portion 18, positive column 22, and anode end portion are encompassed in a tube envelope made of quartz having precision outside and inside dimensions. The use of quartz as the tube envelope is important in terms of the invention because quartz has the lowest loss characteristics to microwave energy of any other known tube envelope material. Thus, the noise energy passes virtually unattenuated through the quartz envelope portion of the positive column 22 within waveguide 14. A quartz tube envelope is also advantageous from the standoint of the tube manufacturing process. Quartz permits going to higher baking temperatures during vacuum processing to more completely out gas the tube envelope. Only high-quality tube manufacturing and processing techniques should be used in constructing the tube 12 to further insure stability and long life by the exclusion of contaminating residual gases.

Heretofer, argon and neon have invariably been used as the gas fill in gas discharge noise tubes. According to the present invention, xenon provides the gaseous medium through which the electron discharge occurs. Xenon has the lowest ionization potential of any of the rare gases, including argon and neon. Consequently, less DC applied voltage is required to initiate an electron discharge.

The low ionization potential of xenon is less than that of residual impurities commonly encountered in gas-filled tubes. Thus, the xenon tube 12 can be operated such that any impurities within the tube envelope are not ionized, and therefore have no effect on the noise power output of the discharge plasma. Furthermore, xenon has a lower critical current" characteristic than argon and neon. Spurious fluctuations and oscillations in the discharge plasma can be avoided while operating at lower DC power levels. Since DC power is required to operate a Xenon-filled noise tube, longer tube life can be anticipated.

Still another advantage incident to the use of Xenon is that it is an extremely heavy gas, in fact the heaviest of the rare gases. Consequently, its rate of diffusion into the tube envelope is extremly low. Since the pressure of the gas fill must remain constant if the noise power generated by the discharge plasma is to remain constant, it is important that the gas fill pressure remain rather precisely constant with age. While it is, of course, good practice to aiways operate the noise standard in a uniform ambient temperature environment, the xenon fill pressure is less temperaturesensitive due to its low-temperature coefiicient.

The pressure of the xenon fill in tube 12 is selected according to the frequency bandwidth of the waveguide 14-, i.e., the frequency bandwidth of the noise power coupled to output port 3%. Another variable to consider is the DC current conducted through the tube 12 by way of the electron discharge. It is desirable to operate the tube 12 at some constant DC current level which is sufficient to, in effect, fully couple to the waveguide the electron discharge, in the sense that further increase in the DC current supplied by the external power supply does not produce any significant increase in the generated noise power level.

The insertion loss of waveguide 1 with the tube 12 in operation, termed hot insertion loss, is a function of the DC current through the tube. It is found that at hot insertion losses above 20 db, the noise power available at output port 34 remains substantially constant. In th r words, the curve of hot insertion loss versus available noise power (P shown in FIGURE 4, is substantially flat above the 20 db point indicated at 45. Accordingly, knowing the frequency bandwidth desired, the xenon fill pressure is selected to give the lowest level of DC operating current necessary to operate on the flat part of the curve (FZGURE 4) to the right of the 20 db point. Thus, operating efficiency is achieved, and yet the available noise power output remains rather constant in spite of minor variations in current and tube fill pressure.

While the tube 12. can be operated such that the available noise power output is reasonably unaffected by slight variations in fill pressure, it is nevertheless desirable to maintain constant tube fill pressure. Further to this end, the cathode end portion 18 of the tube envelope is made substantially larger than in prior art noise tubes. This enlargement serves to provide a gas reservoir of a volume at least ten times and preferably one hundred times the volume of the tube envelope encompassing the active portion or positive column 22 of the tube 12. This increases the ratio of gas fill volume to tube envelope surface, thereby minimizing the effect of diffusion of xenon gas into the tube envelope and other tube parts. Moreover, the increased fill volume renders the fill pressure less sensitive to ambient temperature changes.

Referring to FIGURE 2, the cathode, generally indicated at 50, of the gas discharge noise tube 12 is of the indirectly heated type rather than the cold cathode type invariably used in prior art gas discharge noise tubes. As is shown, the cathode structure includes a cylindrical cathode member 52, preferably of nickel, having an open end facing rearwardly and a closed end facing the anode located at the opposite end of the positive column 22. The cylindrical surface of the cathode member 52 is coated with a suitable oxide 53 having a low work function when heated. The cathode member 52 is conservatively designed for long life. A filament or heater coil 54 is disposed within the cylindrical cathode member 52 for supplying heat to activate the oxide coating 53. The heated or hot cathode used in the gas discharge noise tube 12 of the invention permits further reduction in the DC operating power required. Cathode member 52 and the filament coil 54 are supported within the enlarged cathode end portion 18 in suitable fashion, known to those skilled in the art. Such support may be provided by a glass or ceramic rod 58 sealed in the tube envelope end wall 56. Several of the rods 53 have electrical conductors embedded therein for external electrical connection to the cathode member 52 and filament coil 54.

Still referring to FIGURE 2, the cathode structure 59 further includes a shield 60 in the form of a cylinder having an opening 62 in its front face for the passage of electrons emitted from the cathode member 52. The shield 60 serves to prevent positive ions from impinging on the cylindrical surface of the cathode member 52 and thus preventing premature dissipation of the oxide coating 53. Also, the shield 60 provides for more eflicient heating of the cathode. The shield 66 is supported by the ends of several of the rods 58 projecting into the cathode end portion 18 of the discharge noise tube 12.

Also included within the enlarged cathode end portion 18 of the gas discharge tube 12 is a porous ceramic capsule 64 which contains a getter material for absorbing impurities in the gas fill. According to the invention,

micro-fine uranium particles 66 are confined within the capsule 64 to serve as the getter material. Quartz wool 65 is used to confine the uranium particles 66 to the front section of the capsule 64. Thus, the uranium particles 66 are spaced from the end wall 56 during the process of bonding the capsule 64 to the tube envelope. It is found that uranium particles are considerably more efiective in absorbing impurities than other commonly known getter materials.

In order to provide rigid mounting of the gas discharge noise tube 12 and afford protection against shock, the enlarged cathode end portion 18 is potted within the housing 16 with a suitable material such as epoxy.

The anode end portion of the discharge tube 12 is of conventional construction consistent with long life, familiar to those skilled in the art. It is preferred, however, to make the anode '67 of molybdenum which is known to have a low sputtering rate. The anode 67 should have a large surface area to provide long life. An anode pin 68, formed of a suitably conductive material such as Kovar, mounts the anode 67 and is sealed to the anode end of a tube envelope. A graded seal is employed to make the transition from quartz to a glass which will bond to Kovar. Spring contact 69 engages the anode pin 68 to electrically connect the anode 67 to the mount 10 for grounded anode operation. If desired, the anode can be brought out on a lead (not shown) for electrical connection to the DC power supply.

The double-ended noise standard embodiment of the invention, shown in FIGURE 3, also includes the novel features of the noise source standard of FIGURE 1. The only significant difference in the two enclosed embodiments is that the noise standard of FIGURE 1 has only one output port 34, whereas the standard of FIGURE 3 has two output ports 70 and 72. Since each end of the waveguide 14- terminates in an output port, two diaphragms 38 are necessary to confine the protective gas atmosphere within this OFHC copper waveguide section. The carbon wedge waveguide load 44 incorporated in the mount 10 of FIGURE 1 is not so incorporated in the waveguide mount 10 of FIGURE 3. In its stead, a matched waveguide load is connected externally to one of the output ports in, 72 with the other output port connected to the equipment under test. The gauge 42 monitors the pressure of the protective gas atmosphere in the waveguide 14 just as in the embodiment of FIGURE 1. The xenon gas-filled discharge noise tube disclosed in connection with FIGURE 1 is used in the embodiment of FIG- URE 3. Accordingly, the housing 16 contains the cathode end portion of the discharge tube, and the tubular sections 28 and 32 encompass the positive column of the tube and also serve to mount the tube relative to the waveguide 14 at an insertion angle of 7 degrees.

The double-ended noise standard embodiment of FIG- URE 3 has some advantages over the single-ended embodiment of FIGURE 1 in certain test procedures. For example, the double-ended embodiment is more conducive to tests calling for a comparison of its noise power output with the noise power output of another source, such as a second standard. Since the cold insertion loss of the waveguide 14 is negligible, one of its output ports can be connected to a noise power indicator circuit, while its other output port is connected to the output port of the other noise source. To compare these two noise sources, the gas discharge tube of the double-ended embodiment is energized, and the indication of the noise power output is noted. Then the tube is de-energized, and the noise power output of the other source is coupled through the waveguide 14 to the noise power indicating circuit. Thus, a comparison can be readily had without requiring a complicated waveguide switching network. Such a test procedure is made possible due to the negligible insertion loss of waveguide 14 with the discharge tube of the doubleended standard de-energized.

It will also be appreciated that the double standard is capable of performing concurrent noise tests on separate equipment, since constant noise power output is available at each of its outputs 70, 72.

It is thus seen that all of the features incorporated in the noise source standard of my invention are calculated to provide extremely long life and to maintain precisely constant noise power output over life. It will be appreciated that improvements in this direction can be obtained using any of the features herein disclosed separately or in combination. Thus, for example, the features of the mount 10 could well be used with an argon-filled tube and still obtain improvements over existing noise source standards.

It will also be appreciated that other features can be incorporated. For example, it is contemplated that the elliptical apertures 24, 26 in the waveguide 14 (FIGURE 1) may be choked so as to minimize the effect of their presence on microwave energy conducted through the waveguide. In addition, it is contemplated that the waveguide fianges 39, 40 clamping the diaphragm 38 across the waveguide 14 may also be choked to minimize the elfect of gap between the flanges.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efiiciently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A noise source standard comprising, in combination:

(A) a gas discharge tube having (1) an anode, (2) a cathode spaced from said anode, and (3) an envelope enclosing said anode and cathode in a gas atmosphere,

(a) said envelope having an elongated tubular portion through which electron discharge in said gas atmosphere between said anode and cathode takes place; and (B) a mount including (1) a microwave waveguide having at least one output port, and

(2) a protective gas atmosphere confined within said waveguide to prevent oxidation of the interior surfaces thereof,

(3) said tubular envelope portion of said tube being inserted through said waveguide such that noise energy produced by an electron discharge plasma is coupled into said waveguide for propagation to said output port.

2. The noise source standard defined in claim 1 where- (1) said gas atmosphere within said tube envelope is comprised of xenon gas. 3. The noise source standard defined in claim 1 where- (1) at least said elongated tubular portion of said envelope is formed of quartz.

4. The noise Source standard defined in claim 1 where- (1) said tubular envelope portion of said tube is inserted through said waveguide at an angle of approximately 7 degrees relative to said waveguide.

5. The noise source standard defined in claim 1 where- (1) said waveguide is formed of oxygen-free, highconductivity .(OFHC) copper.

6. The noise source standard defined in claim 1 wherein said mount further includes:

(1) a diaphragm extending transversely across said waveguide adjacent each said output port for confining said protective gas atmosphere therein,

(a) said diaphragm being formed of a material which is substantially lossless to noise energy propagating therethrough.

7. The noise source standard defined in claim 6 wherein said mount further includes:

(1) a gauge for monitoring the pressure of the protective gas atmosphere confined within said waveguide.

8. The noise source standard defined in claim 1 wherein:

(1) said envelope is formed having an enlargement encompassing said cathode of said tube,

(a) the volume of said envelope enlargement exceeding the volume of said tubular envelope portion by at least a factor of ten.

9. The noise source standard defined in claim 1 wherein:

(1) said cathode of said tube is of the hot cathode type.

10. The noise source standard defined in claim 9 wherein said tube further includes:

(1) a shield partially surrounding said cathode.

11. The gas discharge of the noise source standard defined in claim 1 wherein said tube further includes:

(1) a uranium getter disposed within said envelope.

12. The noise source standard defined in claim 1 wherein said waveguide has a single output port, said mount further including:

(1) a waveguide load disposed in said waveguide on the opposite side of said tubular envelope portion from said single output port.

13. A gas discharge noise tube for use in a microwave noise standard, said tube comprising, in combination:

(A) an anode;

(B) a cathode spaced from said anode; and

(C) an envelope enclosing said anode and cathode in a xenon gas atmosphere,

(1) said envelope having an elongated tubular portion formed of quartz through which electron discharge in said xenon gas atmosphere between said anode and cathode takes place.

14. A mount for use in a gas discharge tube noise standard, said mount comprising, in combination:

(A) awaveguide having 1) at least one output port at a termination there- (2) openings formed in spaced broad walls thereof for accepting the insertion of the positive column of a gas discharge tube through said waveguide;

(B) a sealed housing for containing one end portion of the gas discharge tube;

(C) a first tubular section encompassing the portion of the positive column between said waveguide and said housing;

(D) a second sealed tubular section encompassing the remaining portion of the protective column and the other end portion of the gas discharge tube,

(1) said first and second tubular sealed sections being afiixed about said openings in said waveguide such as to support the positive column of the tub at an angle of approximately 7 degrees relative to the longitudinal axis of said waveguide; and

(E) a protective gas atmosphere confined within said waveguide to prevent oxidation of the interior walls thereof.

No References Cited.

JOHN KOMINSKI, Primary Examiner. 

